test: relax redaction for sysroot

sysroot is different when bootstrapping rustc

```
---- expected: tests/testsuite/cfg.rs:444:27
++++ actual:   stderr
   1    1 | [ERROR] output of --print=split-debuginfo missing when learning about target-specific information from rustc
   2    2 | command was: `[ROOT]/compiler/target/debug/compiler[..]--crate-type [..]`
   3    3 |
   4    4 | --- stdout
   5    5 | ___[EXE]
   6    6 | lib___.rlib
   7    7 | [..]___.[..]
   8    8 | [..]___.[..]
   9    9 | [..]___.[..]
  10   10 | [..]___.[..]
  11      - [..]rust[..]
       11 + /checkout/obj/build/[HOST_TARGET]/stage2
  12   12 |
```

https://github.com/rust-lang-ci/rust/actions/runs/9814397548/job/27101968836#step:25:10913

Author: weihanglo

tests/testsuite/cfg.rs

@@ -452,7 +452,7 @@ lib___.rlib
 [..]___.[..]
 [..]___.[..]
 [..]___.[..]
-[..]rust[..]
+[..]
 
 
 "#]])
@@ -470,7 +470,7 @@ lib___.rlib
 [..]___.[..]
 [..]___.[..]
 [..]___.[..]
-[..]rust[..]
+[..]
 [..],[..]
 ___
 123